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Dec. 15, 2011 -- A few years back, a study made headlines by suggesting that weight gain is socially contagious and that people often catch it from their friends.

Now, new research finds that these social interactions may have little impact on body weight, and that early-life family dietary habits and ideas about weight are much more important predictors of adult obesity.

Before making any final decisions, though, one professor doesn’t put too much stock in either study and says more research is needed.

Still, researcher Heather W. Brown, PhD, of Newcastle University in the U.K., says even after taking into account the impact of shared genes, her research suggests that early-life influences such as family eating habits play a big role in adult weight.

“Friends don’t appear to impact weight much, unless they happen to live in the same household,” she tells WebMD. “From a public policy point of view, this suggests that efforts to prevent obesity won’t have much of an effect if they target social networks.”

Weight Gain Contagious? Maybe Not

In 2007, researchers at Harvard University and the University of California, San Diego, first suggested that obesity may be passed like a virus from person to person via social networks, based on their analysis of research on more than 12,000 participants who were followed for 32 years.

They found that friends and even friends of friends were likely to have similar rates of obesity.

The fact that the association was not as strong in neighbors who did not socially interact suggested that shared environment was not the cause.

In their new study, Brown and co-author Jennifer Roberts, of the University of Sheffield, developed their own mathematical model using adult and adolescent sibling data in an effort to better understand the role of genetic predisposition and habits formed during childhood on adult body weight.

They concluded that these influences were far more important predictors of body weight than changeable factors like who was in someone’s circle of friends.

These changeable factors were found to be important only for adolescent siblings still sharing a home.

Critic: ‘Both Studies Flawed’

Indiana University mathematics professor Russell Lyons, PhD, has been highly critical of the 2007 Harvard and University of California study.

Lyons calls the statistical analysis, which led the researchers to conclude that obesity spread within social networks, highly flawed.

In an interview with WebMD, Lyons expressed the same concerns about the new study by Brown and Roberts.

“Some of the issues with this paper are the same as with the earlier research, and some are different,” he says. “But the bottom line is that neither one of these studies tells us much. There really isn’t good research on the impact of social networks on obesity.”